General Science - Physics MCQs
Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examinations.
71. What are ultrasonic sounds?
[A] Sounds of frequencies above 2 KHz
[B] Sounds of frequencies above 20 KHz
[C] Sounds of frequencies above 200 KHz
[D] Sounds of frequencies above 20 Hz
Show Answer
Correct Answer: B [Sounds of frequencies above 20 KHz]
Notes:
Sounds with frequencies higher than 20 kHz are called ultrasonic sound or ultrasound. Ultrasound is produced by dolphins, bats and porpoises.
72. Which of the following is the cause of echo?
[A] When sound is absorbed
[B] When sound is transmitted
[C] When sound is reflected
[D] When sound is refracted
Show Answer
Correct Answer: C [When sound is reflected]
Notes:
If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
73. Which of these parts of the ear responds to sound waves like a microphone’s diaphragm?
[A] eardrum
[B] lobe
[C] fluid in the inner ear
[D] pinna
Show Answer
Correct Answer: A [eardrum]
Notes:
When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates.
74. Which of the following is another unit of frequency?
[A] decibel
[B] cycle per second
[C] metre per second
[D] second
Show Answer
Correct Answer: B [cycle per second]
Notes:
The change in density from the maximum value to the minimum value, again to the maximum value, makes one complete oscillation. The number of oscillations per unit time is the frequency of the sound wave.
75. What is the relationship between the velocity of sound and the pressure of gas when the temperature remains constant?
[A] directly proportional to each other
[B] inversely proportional to each other
[C] independent of each other
[D] None of the above
Show Answer
Correct Answer: C [independent of each other]
Notes:
The velocity of sound is independent of the pressure of gas provided the temperature remains constant.
76. Which of the following is correct about the speed of the sound, at same temperature?
[A] sound travels faster in humid air than in dry air
[B] sound travels slower in humid air than in dry air
[C] speed of sound is same in humid air and dry air
[D] None of the above
Show Answer
Correct Answer: A [sound travels faster in humid air than in dry air]
Notes:
With increase in humidity, density of air decreases. So with rise in humidity velocity of sound increases. This is why sound travels faster in humid air (rainy season) than in dry air (summer) at the same temperature.
77. Which of the following is correct about a Sound wave?
[A] It is a mechanical wave
[B] It is an electromagnetic wave
[C] It is both a mechanical and electromagnetic wave
[D] It is neither a mechanical nor an electromagnetic wave
Show Answer
Correct Answer: A [It is a mechanical wave]
Notes:
Sound is a mechanical wave and cannot travel through a vacuum. It needs a medium to travel.
78. Which of the following represents ideal gas law?
[A] PVT = constant
[B] PT/V = constant
[C] PV/T = constant
[D] VT/P = constant
Show Answer
Correct Answer: C [PV/T = constant]
Notes:
Since PV = constant and V/T = constant for a given quantity of gas, then PV/T should also be a constant. This relationship is known as ideal gas law.
79. What is the S.I. unit of absorptive power?
[A] dioptre
[B] metre
[C] ampere
[D] No unit
Show Answer
Correct Answer: D [No unit]
Notes:
Since absorptive power is a pure ratio it has no units and dimensions.
80. What do we call the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium?
[A] Equilibrium point
[B] Triple point
[C] Normal point
[D] None of the above
Show Answer
Correct Answer: B [Triple point]
Notes:
the triple point is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium.
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